Apparatus for shearing the edges of a sheet of metal

ABSTRACT

A method of and apparatus for shearing the edges of a sheet of metal in which a sheet is positioned with its longitudinal axis effectively parallel to the cutting line of shears, the sheet is moved towards the cutting line, that edge of the sheet adjacent the shears is cut, the sheet is rotated through 180* about an axis parallel to the cutting line and the other edge of the sheet is moved towards and cut by the shears, wherein the sheet is initially positioned relative to the shears in dependence on the deviation of the edges to be cut from linearity, the deviations being calculated using detectors which detect the positions of the edges adjacent and remote from the cutting line as the sheet is moved towards the shears.

United States Patent 11 1 Lhenry 1 June 24, 1975 1 1 APPARATUS FOR SHEARING THE EDGES OF A SHEET OF METAL [75] Inventor: Bernard Lhenry, Le Creusot,

[30] Foreign Application Priority Data Oct. 26. 1972 France 72-38005 [52] U.S. Cl. 83/71; 83/36; 83/73; 83/364; 83/367; 83/410; 83/422 [51] Int. Cl. B65h 9/00 [58] Field of Search 83/36, 410, 422, 418, 421, 83/364, 367, 370, 372, 71, 73

3,297,173 1/1967 Schott 83/410 X 3,592,095 7/1971 Passa et a1. 83/410 X 3,768,101 10/1973 Kuts 83/422 X 3,788,174 1/1974 Morse et a1 83/422 X Primary ExaminerFrank T. yost Attorney, Agent, or Firm-Cameron, Kerkam, Sutton, Stowell & Stowell [57} ABSTRACT A method of and apparatus for shearing the edges of a sheet of metal in which a sheet is positioned with its longitudinal axis effectively parallel to the cutting line of shears, the sheet is moved towards the cutting line, that edge of the sheet adjacent the shears is cut, the sheet is rotated through 180 about an axis parallel to the cutting line and the other edge of the sheet is moved towards and cut by the shears, wherein the sheet is initially positioned relative to the shears in dependence on the deviation of the edges to be cut from linearity, the deviations being calculated using detectors which detect the positions of the edges adjacent and remote from the cutting line as the sheet is moved towards the shears.

+ oooooo/ooooop SHEET PATENTEDJUN 24 I975 s QUE a Q R m N: mi h APPARATUS FOR SHEARING THE EDGES ()F A SHEET OF METAL The present invention relates to a method of and apparatus for automatic shearing of the edges of a sheet, particularly of metal, for providing a sheet with parallel edges.

In accordance with one aspect of the invention, there is provided a method of shearing the edges of a sheet of comprising:

a. positioning the sheet adjacent shears with the longitudinal axis of the said sheet effectively parallel to the cutting line,

b. advancing-the sheet towards the shears in a direction perpendicular to the cutting line to cut that one edge of the sheet adjacent the shears,

c. as the one edge passes over two references situated at a distance r from a reference line, measuring the distances E and F from the reference line of two points and e adjacent the ends of the other edge and situated on perpendicular of the cutting line passing through the said reference,

(1. calculating the distances E r and F r,

e. positioning the points 2 and 2 respectively at distances /z(] E r) and /2(1 F r) from the reference line, I being the desired width of the sheet after cutting,

f. operating the shears to cut the sheet,

g. withdrawing the sheet from the shears,

h. turning the sheet through 180 about an axis parallel to the cutting line,

i. advancing the second edge sheet towards the shears with the other edge adjacent the shears and positioning the points of the cut edge opposite the points 0 and e at a distance [from the reference line.

j. operating the shears to cut the sheet, and

k. withdrawing the sheet from the shears.

in accordance with another aspect of the invention, there is provided a method of shearing the edges of sheet comprising:

a. positioning the sheet adjacent the shears with the longitudinal axis of the sheet effectively parallel to the cutting line,

b. measuring, with respect to a reference line, the dis tance of extreme points e and e adjacent the ends of the edge of the sheet remote from the cutting line,

c. measuring, with respect to a reference line, the distance of at least one intermediate point on the edge of the sheet remote from the cutting line,

d. calculating, as a function of the distance of the extreme points and the intermediate point, the departure from linearity of the edge of the sheet remote from the cutting line,

e. advancing the sheet towards the shears,

f. as the edge adjacent the cutting line passes extreme references situated with respect to the cutting line to one side of the said points and at a distance r therefrom, measuring, with respect to a reference line, the distances of the extreme points e and e,

g. as the edge adjacent the cutting line passes inter mediate references situated at a distance r from the cutting line and to one side of the intermediate point, measuring, with respect to the reference line, the distance of the extreme points e and e,

h. calculating, as a function of the distances of the extreme points on passage of the edge past the extreme and intermediate references, the departure from linearity of the edge of the sheet adjacent the cutting line,

i. calculating the width of sheet to one side of each point e and a, subtracting from each width the ultimate differences resulting from non-linearity of the edge so as to obtain the width which can be used, subtracting the final width so as to obtain the total reduction in width required,

j. advancing the sheet towards the shears, positioning the points 0 and e with respect to the reference line, at distances equal to: final width half total reduction difference of the edge remote from the cutting edge, corrected by the distance between the reference line and the cutting line,

k. operating the shears to cut the sheet,

1. withdrawing the sheet from the cutting line,

m. turning the sheet through about an axis parallel to the cutting line,

n. advancing the sheet towards the shears, positioning the cut edge, with respect to the reference line, at a distance from the reference line equal to the final width of the sheet corrected by the distance between the reference line and the cutting line.

0. operating the shears to cut the sheet, and

p. withdrawing the sheet from the shears.

In accordance with a further aspect of the invention, there is provided apparatus for shearing the edges of a sheet comprising:

a. an edge shearer,

b. a table adjacent the shearer provided with rollers for supporting a sheet,

c. means for moving a sheet perpendicularly to the cutting line of the shearer,

(:1. means for rotating a sheet adjacent the shears, after cutting a first edge of a sheet, and

e. means for controlling operation of the apparatus.

Preferably the apparatus comprises:

a horizontal table provided with rolling elements at moval of the said sheet,

at least two carriers, movable in a direction perpen dicular to the cutting line, I

means for gripping one edge of the sheet, mounted at an extremity on that side of each carrier adjacent the shearer,

motors for linear movement of the carriers,

means for withdrawing a sheet after the first cut from the shearer,

detectors for detecting the passage of the edge of a sheet adjacent the cutting line, situated equidistantly from the cutting line in the direction of motion of a carrier,

detectors mounted on the gripping means and operable by that edge of a sheet remote from the cutting line for controlling advance of the carriers,

position coders for the detectors with respect to the cutting line,

a sequential automatic control for motors for the shearer, the table and the return means,

a numerical control unit for controlling positioning of the carriers according to signals from the coders and detectors, and the desired width of the sheet.

The method and apparatus may, for example, be used for cutting off the edges of a metallic sheet with rough edges, after laminating and heat treatment. They may also be used for cutting off a part of any material.

Embodiments according to the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. I is a plan view of an apparatus according to the invention;

FIG. 2 is a section on the line A-A of FIG. 1;

FIG. 3 is a section on the line B-B of FIG. 1;

FIG. 4 is a section on the line CC of FIG. 1;

FIGS. 5 to 9 illustrate different stages of operation of the apparatus of FIG. 1;

FIG. 10 illustrates diagramatically a first method in accordance with the invention;

FIG. 11 illustrates diagramatically a second method in accordance with the invention; and

FIG. 12 shows a simplified diagram of the control assembly of the apparatus of FIG. 1.

As shown in FIGS. 1 to 4, the apparatus comprises a sheet metal support table 8 formed by rollers 81 arranged with their axes horizontal, and a shearer 7 arranged laterally with respect to the table 8. The shearer, for cutting the edge of a sheet, comprises a cutter 71 which is movable along cutting line 72, and a pressure plate 73 which presses the sheet to be cut against table 74. The roller table 8, which the sheet parallel to the cutting line 72, can be connected with a feed table with rollers on the supply side and with a removal table with rollers on the output side. The rollers 81 are driven by motors 82. The sheet can be displaced perpendicularly to the cutting line 72 by positioning assemblies 1, 2, 3 and 4. The positioning assemblies 1, 2, 3 and 4 each comprise a carrier 11, 21, 31, 41 movable along and guided by a slider extending parallel to the rollers 81, and gripping means or spike 12, 22, 32, 42 extending towards the shearer 7.

The positioning assemblies 1, 2, 3, 4 each include a driving motor 161, 261, 361 and 461, which ensure movement parallel to the rollers 81. Each of the motors 161, 261, 361, 461 drive a respective carrier through a pinion 18, 28, 38, 48 engaging with a transverse rack 15, 25, 35, 45, fixed to the framework of the table 8 (FIG. 5). In addition the motors drive coders 17, 27, 37, 47 respectively which mark or indicate the position of the respective assembly with respect to the cutting line 72. Each of the spikes 12, 22, 32, 42 is provided with a contact 131, 231, 331, 431 respectively, which on making contact in the open position with the sheet metal, controls the pressure and grasp of the edges of the sheet by a jack not shown. Contacts also operated by the sheet edge before complete engagement control the slowing down. The energy supply of each of these feed assemblies is provided through a guide cable such as 28'. The displacement in a transverse direction of the sheet metal by the feed assemblies is facilitated by roller elements 83 which are arranged with their axes parallel to the cutting line and are vertically movable under the action of hydraulic jacks controlled by electric valves, the roller elements lifting the sheet metal above the rollers 81. Each spike is vertically movable with respect to its carriage so as to come to the level of the roller element 83. After cutting the first side of the sheet, the sheet is turned through 180 by turning means 14 comprising open ended ducts 144 connected to a vacuum pump and carried on beams 143 which are pivotable through 180 about a horizontal axis under the action of a rotary jack. The pivotable beams 143 are mounted at the end of horizontal arms 142 fixed on a cross-piece 145 extending parallel to the cutting line 72 and fixed to two lateral carriers 141 adjustable vertically along two lateral columns 146. Pivoting of the beams 143 is effected when the arms 142 ofthe assembly are in a raised position at a height H above the table 8 which is at least equal to half the maximum width of a sheet of metal.

The operation of the apparatus will now be described with reference to FIGS. 5 to 9.

Initially the operator energises the motors 82 of the roller table 8 and of the associated table on the feed side to feed a sheet P on to the table 8. After passage of the sheet P over a stop situated on the feed side of table 8, the feed side table stops and table 8 goes into reverse, the sheet metal returning towards the stop. When the sheet P reaches this stop, table 8 stops. The sheet P is then correctly positioned for entry under the shears of the shearer.

The operator then selects, depending on the length of the sheet P, which of the spikes 22, 32 or 42 to use to grip the sheet, spike 11 on the feed side always being used. The required width of metal to be obtained is then introduced into the numerical control and the operator starts the automatic operating cycle.

The roller elements 83 rise and lift the sheet metal above the rollers 81 of the table 8. The electric control valves of control jacks for the spikes are adjusted and the spikes rise accordingly. Spike l2 and the selected spike (spike 42 in the case of FIG. 5) advance towards the sheet P, slow down as they approach and engage the edge of the sheet, spikes l2 and spike 42 engaging the sheet at the points e and e of the edge II remote from the cutting line 72. The two spikes then take up position parallel to the cutting line 72 at a distance therefrom equal to the desired width, increased by a guard distance. The intermediate spikes 22 and 32, situated between the extreme spikes 12 and 42 holding the sheet advance (FIG. 5) and the engage the sheet edge II at the points i and i.

In the case ofa concave edge, the difference in position between an extreme spike and the nearest spike will be recorded in the memory of the numerical control. In the case shown in FIG. 5 this difference is represented by the difference A B d and by the difference D C= (1,. It is an advantage for the two and end spikes to be positioned parallel to the cutting line because it then follows that D A.

Spikes 22 and 32 then return to their initial positions. The extreme spikes l2 and 42 then move the sheet forward, and sheet edge I actuates in passing, in the position shown by the full lines in FIG. 6, detectors l9 and 49 which serve as reference for the calculation of the dimensions. The values given by the coders 17 and 47, E and H respectively, are retained in the memory. Sheet P continues to advance and, if the edge is concave, it actuates detectors 29 and 29 in the position shown by the dotted lines in FIG. 6. At this time, the values of the codes 17 and 47 with respect to the cutting line 72 are F and G respectively.

One of several methods for the positioning of the sheet metal for cutting edge I can be next used. In the various methods, the widths of the uncut sheet to the right of the two extreme points e and e are first calculated. These true widths L and L, to the left of the extreme contact points e and e, are determined by subtracting the value r (distance between the cutting line and the detectors) from the distances E and H respectively. In one method the edge differences are defined to the right of the intermediate spikes. They are shown in FIG. 10 and in Table l below. The values A B =dand D (1 define the difference at edge ll. The values E F d, and H (i=1! define the difference at edge I. By subtracting from the widths L and L the final differences at the edges, d, and 11 respectively for L and a, and d 2 for L. the effective widths U and U of the sheet P (FIG. 10) are obtained. From these effective widths the final width l is subtracted and so the widths of total reduction are obtained, to the left of e and e, which are divided by two to share them between the two edges. Positioning is complete. as is seen in FIG. 7, when the points e and a respectively are at a distance, with respect to the cutting line 72, equal to:

I half reduction edge error d (for e), and

I half reduction 0 edge error 11 (for e) or L'- half reduction 0' edge error al (for e), and

L half reduction 0 edge error d, (for e). The final width 1 is equal to the true width,'less two half reductions, less'the error at edge I. Positioning will be complete (FIG. 7) when the coders l7 and 47. read the values given in Table l.

carriage which holds the cutting edge of the. shears moves backwards to the end of the return stroke. The return cycle is effected by the air ducts 144 below or above the sheet. The roller elements 83 and the end spikes 12 and'42 rise again. The selected spikes l2 and 42 again advance towards the sheet P and close (FIG. 8). They move the sheet P forward until the cut edge I ispositioned at a distance equal to the final width T from the cutting line 72. The roller elements 83 drop downwards and edge ll is cut in the same way as edge 1. After cutting, the roller elements 83 raise the sheet which is then drawn back by spikes 12 and 42, in such a manner as to be released from the shears and to be positioned for removal. Spikes l2 and 42 then open and move backwards at the end of the return stroke. Roller elements 83 retract to rest the sheet on the roller table 8. The sheet can then be removed.

It is evident that if the length of the sheet p does not necessitate spikes other than 12 and 22, there is no calculation of edge error. Positioning of the extreme spikes is then effected at distances MI E r) and- /2(l F r), E and F being the distances of the ex- Divergence from straight line of Positioning of After positioning of the sheet P. the roller elements 83 are retracted, pressure jacks are operated to move plate 73 downwards to hold the sheet on the table 74. The cutter of the shears is then operated to cut the sheet metal. At the end of the stroke of the cutter, the pressure jacks and plate 73 rise and the roller element 83 lift the sheet metal. The spikes l2 and 42 draw back so that the axis of the'sheet coincides with the axis of the turner l4 (FlGfSl. The extent of withdrawal of spikes 12, 42, calculated by, the numerical control, is equal to the distance d between the axis of the turner and the cutting line 72, less half the final width of the sheet. The distance (I must be sufficiently larger than the value of half the maximum width in order to release thesheet from the shears. when positioning is complete, spikes l2 and 42 open to release the sheet and withdraw at th'eend of the return stroke. The roller elements 83 drop down again and rest the sheet on the rollers of table 8. The return cycle is carried out whilst the treme spikes l2 and 22 when edge I passes over the detectors 19 and 29.

In the above method, the edge differences are de fined to the right of the intermediate spikes. There are however other methods for the calculation of the edge differences. For example, the edge differences can be defined with reference to the medium axis between the displacement axes of the extreme spikes. As in the previous calculation, the extreme spikes are positioned parallel to the cutting line (FIG. 5) and the intermediate spikes come into contact with edge II. The differences at the middle of edge [I can then be calculated starting from the determined distances A, B, C, D, of the coders and distances between carrier axes given on H0. 11. The sheet then moves forward to determine the distances E, H, on passing by the extreme detectors 19 and 49, and F, G, on passing by the intermediate detectors 29, 39. Table ll below gives the values of the differences at the middle of the sides.

TABLE 11 Calculated from the \ulues of the coders of the extreme spike on the feed side and the intermediate The calculation of the utilisable width at each extremity of the sheet and the positioning of the spikes for cutting can then be effected by correction of the true widths using the different edge differences, taking the largest edge differences, etc.

The control head of the apparatus is shown in summary form in H6. 12. It comprises an automation unit 6 with a programmer ensuring operation in correct sequence of the motors of the apparatus, and a numerical control unit which ensures positioning of the spikes, in accordance with one of the above methods, as a function of the dimensions of the original sheet, the edge differences and the desired width of the sheet.

The automatic cycle is effected by a step-by-step programmer 9. A housing carrying cams moves by successive steps in front of a series of contacts which control either the electric valves controlling the different jacks, or a series of contacts 52 each one controlling a positioning sequence by the numerical control 5. The housing is caused to pass from one position to the next by closure of the position contacts of the automation unit which establishes the end of the sequence in question or by a signal of completed positioning given by the numerical control.

Assuming the extreme spike on the output side is selected, the cycle is started by operation of a switch 61, the automation 6 introducing into the numerical controls the necessary orders via contacts 53. As edge 1 approaches, contacts 132, 232, 332 and 432 are adjusted and commence the slowing down of the spikes by contacts 541, 551, 561, 571. After this edge I is completely engaged, contacts 131, 231, 331, 431, are pushed in. Contacts 542, 552, 562, 572 are adjusted and control the stopping of the oscillators.

' Variable frequency impulses are transmitted in an automatic cycle from the numerical control towards the inputs of the translators 162, 262, 362, 462 which control the hydro-electric motors 161, 261, 361, 461. The translators ensure the automatic operation of the hydro-electric motors by interpreting the impulses emitted by the oscillators of the numerical control. They also permit control of the motors under manual operation, starting from the impulses emitted from their internal oscillators.

For each positioning sequence, the numerical control unit, using the desired width introduced by printer 51, the values provided by the codes 17, 27, 37, 47 and the signals coming from the detectors 19, 29, 39, 49, calculates a position to be reached. The impulses transmitted to the inputs before or after the control transla- 6 tors of the motors of the extreme carriages are provided gy a multi-stage frequency oscillator. Knowing the position to be reached and the coder position at any instant, the numerical control determines the instant distance to go and compares it with a range of speeds which are predetermined and introduced into the memory. When the distance to go is greater than all of this range, the oscillator operates at the highest frequency corresponding to the highest motor speed. When the distance to go becomes less than the first level, the oscillator operates at a lower frequency, etc.

Finally, the impulses are cut down at 1 mm from the position to be reached so as to allow for the lag of the hydro-electric motor.

It will be appreciated that if the opposite sides of the initial sheet are effectively parallel (S type sheet), the calculation of the difference for edge ll can be used on its own for determination of the effective sheet widths.

The above described method and apparatus enable a user to obtain a sheet with opposite edges parallel, with a predetermined width; it is possible to effect automatic shearing of a piece of sheet metal with sides altered over a great length in either a concave or convex manner.

I claim:

1. Apparatus for shearing the edges of a sheet comprising:

an edge shearer,

a table adjacent the shearer for supporting a sheet,

at least one carriage guided for movement in a direction perpendicular to the cutting line, means for gripping an edge of a sheet, the gripping means being mounted at an extremity of at least one carriage on that side adjacent the shears,

motor driving means for linear displacement of each carriage in opposite senses,

means for rotating a sheet adjacent the shears, after cutting a first edge of a sheet,

detectors for detecting the passage of the edge of a sheet adjacent the cutting line, each situated at an equal direction from the cutting line in the direction of displacement of a carriage, detectors mounted at the end nearest to the shears of each carriage operably by the edge of a sheet remote from the cutting line for controlling the advance of the carriage in relation to the said edge,

position coders for controlling position of each carriage,

and means for controlling operation of the apparatus.

2. Apparatus in accordance with claim 1, wherein the rotating means comprises a plurality of horizontal arms fixed to a member which is vertically movable and each provided at its extremity with a pivotable sheet gripping means.

3. Apparatus in accordance with claim 1, wherein the table comprises roller elements for displacement of the sheet perpendicularly to the cutting line, motor means for vertical moving of said roller elements between a low position under the table and a raised position above the table, and motor means for vertical moving of said gripping means.

4. Apparatus in accordance with claim 3, wherein the table comprises roller elements for displacement of the sheet in a direction parallel to the cutting line, motor driving means for said roller elements, and means to control said motor driving means as a function of the position of the sheet in said direction.

5. Apparatus in accordance with claim 3, comprising:

a sequential automated control for the driving means of the table, the shears, the rotating arrangement, and a numerical control unit,

a numerical control unit for positioning each carriage as a function of the signals from at least one coder and of the final width of the sheet and for causing the change of sequence of the sequential automated control.

6. Apparatus in accordance with claim 1, comprising:

a numerical control unit for positioning each carriage as a function of the signals from at least one coder and of the final width of the sheet.

7. Apparatus in accordance with claim 1, comprising:

a sequential automated control for the shears, the sheet rotating means, and a numerical control unit,

a numerical control unit for positioning each carriage as a function of the signals from at least one coder and of the final width of the sheet and for causing a change of sequence of the sequential automated control.

8. Apparatus in acordance with claim 7, wherein the numerical control unit comprises means for calculating at least a value of the departure from linearity of the edge of the sheet adjacent the cutting line and at least a value of the departure from linearityy of the edge of the sheet remote from the cutting line.

9. Apparatus in accordance with claim 7, wherein the sequential automated control comprises means for selecting the number of gripping means in operation according to the length of the sheet.

10. Apparatus in accordance with claim 9, wherein the sequential automated control comprises means for driving the advanced of the two extreme carriages selected and for driving the gripping means of the said carriages and means for driving the advance of each intermediate carriage as far as the edge, remote from the cutting line.

11. Apparatus in accordance with claim 9, wherein the numerical control unit comprises means to calculate the width at each extremity of the sheet as a function of the signal of each extreme coder when a signal is given by an extreme detector for detecting the passage of the edge of a sheet adjacent the cutting line.

UNETED STATES PATENT OFFICE QETIFICATE 0F CORRECTION PATENT NO. 3' 890 I 862 DATED June 24 1975 INVENTOR S) 2 Bernard Lnenry it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

[SEAL] Claim 1, column 8 line 54 "direction" should -clistance-.

En'gncd and Scaled this sixteenth Day 0fv September 1975 A ttes t:

C. MARSHALL DANN RUTH C. MASON (ommissimu'r uj'Parenls and Trademarks Arresting Officer 

1. Apparatus for shearing the edges of a sheet comprising: an edge shearer, a table adjacent the shearer for supporting a sheet, at least one carriage guided for movement in a direction perpendicular to the cutting line, means for gripping an edge of a sheet, the gripping means being mounted at an extremity of at least one carriage on that side adjacent the shears, motor driving means for linear displacement of each carriage in opposite senses, means for rotating a sheet adjacent the shears, after cutting a first edge of a sheet, detectors for detecting the passage of the edge of a sheet adjacent the cutting line, each situated at an equal direction from the cutting line in the direction of displacement of a carriage, detectors mounted at the end nearest to the shears of each carriage operably by the edge of a sheet remote from the cutting line for controlling the advance of the carriage in relation to the said edge, position coders for controlling position of each carriage, and means for controlling operation of the apparatus.
 2. Apparatus in accordance with claim 1, wherein the rotating means comprises a plurality of horizontal arms fixed to a member which is vertically movable and each provided at its extremity with a pivotable sheet gripping means.
 3. Apparatus in accordance with claim 1, wherein the table comprises roller elements for displacement of the sheet perpendicularly to the cutting line, motor means for vertical moving of said roller elements between a low position under the table and a raised position above the table, and motor means for vertical moving of said gripping means.
 4. Apparatus in accordance with claim 3, wherein the table comprises roller elements for displacement of the sheet in a direction parallel to the cutting line, motor drivIng means for said roller elements, and means to control said motor driving means as a function of the position of the sheet in said direction.
 5. Apparatus in accordance with claim 3, comprising: a sequential automated control for the driving means of the table, the shears, the rotating arrangement, and a numerical control unit, a numerical control unit for positioning each carriage as a function of the signals from at least one coder and of the final width of the sheet and for causing the change of sequence of the sequential automated control.
 6. Apparatus in accordance with claim 1, comprising: a numerical control unit for positioning each carriage as a function of the signals from at least one coder and of the final width of the sheet.
 7. Apparatus in accordance with claim 1, comprising: a sequential automated control for the shears, the sheet rotating means, and a numerical control unit, a numerical control unit for positioning each carriage as a function of the signals from at least one coder and of the final width of the sheet and for causing a change of sequence of the sequential automated control.
 8. Apparatus in acordance with claim 7, wherein the numerical control unit comprises means for calculating at least a value of the departure from linearity of the edge of the sheet adjacent the cutting line and at least a value of the departure from linearityy of the edge of the sheet remote from the cutting line.
 9. Apparatus in accordance with claim 7, wherein the sequential automated control comprises means for selecting the number of gripping means in operation according to the length of the sheet.
 10. Apparatus in accordance with claim 9, wherein the sequential automated control comprises means for driving the advanced of the two extreme carriages selected and for driving the gripping means of the said carriages and means for driving the advance of each intermediate carriage as far as the edge, remote from the cutting line.
 11. Apparatus in accordance with claim 9, wherein the numerical control unit comprises means to calculate the width at each extremity of the sheet as a function of the signal of each extreme coder when a signal is given by an extreme detector for detecting the passage of the edge of a sheet adjacent the cutting line. 